I Have A Slight Astigmatism Is It Normal To Be Prescribed Weaker Contact Lenses?

Being prescribed a weaker precription is not usually due to astigmatism (although it can seem like that – see below). The main cause of the contact lens prescription being different to the spectacle prescription is the fact that the contact lenses sit on the cornea (i.e. the Back Vertex Distance is zero), whereas the spectacle prescription is taken at a further distance from the cornea (approx 10-14mm Back Vertex Distance). This back vertex distance influences the prescription so those who are short-sighted have contact lens prescriptions weaker than their specs, and those who are long sighted have contact lens prescriptions that are stronger than their specs.
An astigmatism means you have 2 different presciptions perpendicular to each-other, i.e. your prescription might read -2.50 / +0.50 x 180 (the 2nd two numbers representing the astigmatism), which means you have a -2.50 prescription in one direction (along 180 axis), and a -2.00 prescription in the other direction (along the 90 axis). What the optician will do is normally choose a prescription in between the the powers for low astigmatism (in this example, -2.25), or if the astigmatism is strong they will order you a toric lens.